The invention concerns a crane with a telescopic boom whose segments, which can be telescoped out of a base boom with a boom guide piece, are locked in their extended or retracted positions by locking pins, and after the release of the locking pin connectors, can be extended and retracted with a single-stage hydraulic piston-cylinder unit, one end of which is fastened to the boom guide piece with two strokes so that each segment which is to be extended or retracted is coupled either with the inside or with the outside end area of the movable portion of the piston-cylinder unit.
From DE 198 24 671 A1, a telescopic boom of this type is known, in which either the piston rod or the cylinder of the piston-cylinder unit is attached to the attachment piece and the movable part of the piston-cylinder unit, namely in some cases the cylinder and in other cases the piston rod, is provided at its inner and outer ends with a securing and locking unit which can be coupled with grooves in the telescoping segments. If the securing and locking unit is located on the piston rod on the boom securing part, it is provided at its front end with a guide and pulling device running parallel to the cylinder which, at its inner end, carries a securing and locking unit.
The known telescopic boom therefore has a relatively complex design so that, on the inner and outer end of the cylinder and on the outer end of the piston rod and on the inner end of a guide and pulling device connection with it, securing and locking units are placed, which must therefore be present in duplicate.
The problem to be solved by the invention is, therefore, to create a crane with a telescopic boom of the type indicated at the beginning, which has a simpler structure.
According to a first embodiment, this problem is solved, according to the invention, by the fact that, with the piston rod fastened to the boom guide piece, a movable ring or a movable sleeve is guided on the cylinder with a coupling device to couple to the segments which can be locked both to the inner and the outer end area of the cylinder.
The movable coupling device can, in this connection, consist of two opposed pistons which can move in and out, which move in corresponding grooves or holes in the segments and which are known from EP 0 661 234 A1. The pin connections, which lock together the individual segments, can also be designed in such a manner as described in EP 0 661 234 A1. Furthermore, the movable ring or sleeve, which bears the coupling device, can also be provided with a device to unlock the pin connections which lock the individual segments together, as also described in EP 0 661 234 A1.
The telescopic boom in accordance with the invention makes it possible to move the individual segments upward and inward in two strokes, so that more favorable piston-cylinder units with respect to weight can be used, which also have a lower sensitivity to bending. The movable ring or the movable sleeve on the cylinder, which can surround the cylinder only partially, is locked to the cylinder in the end positions through known locking devices. In order to achieving locking and in order to release the locking and in order to move the coupling pins in and out and to move the devices which release the pin connections of the segments between themselves, hydraulic cylinders are provided, as an example, where the movable ring is provided with supply pipes.
An additional hydraulic cylinder can also be used to supply the locking unit, which simultaneously serves to move the locking unit onto the cylinder casing.
In order to make it possible to move the segments in and out in two strokes, these have in their central areas locking holes in which the arresting pin connections reach into the segments in a half-extended position. The distance of the locking holes of the individual segments from the central holes for the inner and outer holes correspond at the same time to the displacement length of the ring or sleeve on the cylinder.
According to another embodiment, the problem is solved according to the invention by the fact that when the cylinder is fastened to the boom guide piece with the outer end of the piston rod, a pipe concentric with the cylinder or lines parallel to it are fastened, which surround the cylinder and that on the pipe or the struts a movable ring or a movable piece is guided with a coupling device which can be coupled to the inner and outer end regions of the pipe or of the lines. At the same time, the ring or the movable piece is again provided with devices to release the locking pin connections corresponding to the first embodiment. Furthermore, the ring or the moving piece is provided with an energy supply which may consist of piping brought with it.
The oil supply for the locking unit as well as the moving unit can also be carried out through telescoping pipes inside the cylinders or through hoses.
If the ring or the sleeve or the moving part which bears the coupling device is not coupled to a segment during the movement of the moving part of the piston-cylinder unit, it is necessary to move it to the other end of the moving part and to lock it again there. For this purpose, in a further embodiment of the invention, a device is provided which retracts the ring or the moving part together with the coupling device from its outside position into the inside position, or vice versa.
It is advantageous to provide the cylinder casing or the pipe enclosing it, or the guides on its outer and inner end regions, with collars, shoulders or grooves with which the rings, sleeves or moving pieces can be connected releasably, for example, using claws or pins.
The guides can be provided with coupling devices with which the moving piece can be connected releasably, using counter-coupling devices.